The present invention generally relates to position measurement of an actuation device and, more specifically, to methods and apparatus for sensorless position measurement of an actuation device using inductance variation.
There is a broad range of solenoid-based actuation devices used in the aerospace industry. The prime purpose of these devices is either to deliver motion or to use the mechanical stroke for controlling secondary electric, gas or fluid substances. The motion results from energizing the coil of the solenoid with current. One class of these devices has the relatively simple task associated with only two end positions. Other devices have to maintain accurate position at any point between the end positions. Regardless of the system implementation in most of the cases, the actual position of the actuation device is required to be known and fed back to the controller. In many applications, this information is vital to proper system operation. Furthermore, the knowledge of the position is often a matter of safety concerns.
There are numerous applications in which the exact position of an actuation device is required for control or protection. Conventional measurement methods use position-sensing devices that have different levels of complexity and cost. These conventional devices require additional hardware, such as interface cables for signal transfer to the controller and supply lines for sensor excitation. Additional signal condition and interface connectors are also required. This additional hardware increases the cost of the systems, reduces reliability and limits the applicability of these devices due to environmental constraints on the sensors.
There are a broad range of solenoid-based actuation devices. Linear actuators are used for linear positioning or transfer of linear force. Rotary actuators are used for rotary positioning or transfer of force. Contactors are used for control and protection purposes of high-power electric substances. Relays are used for control and protection of low-power electric substances. Valves are used for control and protection of gasses and fluids. Electromechanical brakes are used for many applications, including airplane brakes. Electromechanical clutches are devices used for mechanical engagement and disengagement of rotating shafts. The above list of solenoid-based actuation devices covers the commonly used devices.
Referring to FIG. 1, there is shown a schematic diagram of a conventional control system for a solenoid-based actuation system 10 for positioning a controlled substance 26. The actuation system 10 includes a controller 12 and an actuation device 14. A solenoid 16 may be part of the actuation device 10 and may be controlled by a solenoid driver 18, such as a PWM converter, via a solenoid control feeder 28. Positional information may be measured by a position sensor 20 and transferred back to the controller 12 via a sensor cable 22. A sensor conditioner 24 may then condition the signal as necessary for processing by the controller 12. Sensor cable 22 may contain supply or excitation lines required for operation of the position sensor 20. The position sensor 20, the conditioner 24 and the interface hardware imposes a penalty on overall system cost, reliability and applicability of the actuation device for various applications that operate in a more challenging environment.
U.S. Pat. No. 5,583,434, issued to Moyers et al., discloses methods and apparatus for monitoring armature position in direct current solenoids. A special device and circuit are used in order to generate and introduce alternating current required for the measurement. Moreover, the method of the '434 patent uses sinusoidal measurements, thereby requiring two sensors to measure current and voltage. Furthermore, in order to get the desired data, complex calculations are required of the measured values.
As can be seen, there is a need for an improved position measurement method and apparatus for actuation devices. Furthermore, there is a need for an improved actuation device position measurement method and apparatus that eliminates the need for a dedicated sensor and the associated interfaces within the controller.